The Geology of Texas - Vol. 1

Taylor group

Nomenclature. — When this and many other Texas rock groups were named the conception of type locality did not exist. The name of the formation might be changed, because of preoccupation or convenience, and another name substituted without the notion that the conception of the formation was thereby altered. Towns were few, and often one was selected on the strip of the formation because it was the nearest available name, not because the town stood on a large or significant exposure. 55 It is here assumed that for certain names of long standing, change of name does not involve change of the type locality, so that the type locality of the Taylor is on the Colorado in Travis County, the type locality of the Buda on Shoal Creek at Austin, the type locality of the Edwards on Barton Creek near Austin.

The Taylor, first called the "Blue Bluffs division" (from Blue Bluff of the Colorado, 6 miles east of Austin) in Hill's 1889 papers, was named the Taylor marls by Hill(780, p. 73) in1891. In many papers it had been called the "Exogyra ponderosa marls" or "clays."  It changes facies rapidly along the outcrop across Texas, and the attempt to apply the system of formational and member names to these many types of lithology has resulted in a maze of local names.

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Stratigraphic position and contacts. — As was previously stated, the Austin-Taylor contact is unconformable in south-central Texas.  The contact has not been sufficiently studied in west Texas. The Taylor-Navarro contact, according to Stephenson, is represented by a large unconformity from Travis County southwards; at Kimbro, the two basal Navarro zones (Exogyra cancellata zone, and Nacatoch sand) are absent, and the succeeding chalky marl member rests on Taylor with only a thin phosphatic pebble zone intervening. In an exposure 8 miles west of Cameron, Milam County, the Nacatoch sand is absent, and the chalky marl member rests on the Exogyra cancellata zone of the basal Navarro. The unconformity, with the two basal Navarro members missing, "continues toward the southwest with as great or greater magnitude, nearly to the Rio Grande Valley, where, in the vicinity of Eagle Pass, Maverick County, the gap is only partly filled by the Olmos, a coal-bearing formation.  How far this unconformity extends into Mexico has not been determined."

Facies. — Since the foregoing multiplicity of "formations" or members in the Taylor represents an attempt to designate different lithologic facies by individual names, the facies of the Taylor are evidently many. They can be classed mostly as chalks, clays or marls, and sands, but these types of sediments are interpenetrating at many places and at many levels. It is now practically useless to attempt broad generalities concerning the detailed location of each facies during all of Taylor time. At and above the middle of the Taylor in the central Texas outcrop, there was a widespread epoch of sand deposition, represented by the Wolfe City, Durango and unnamed sands. These are marginal, and indicate proximity to a shore. Some levels in the San Miguel in the Eagle Pass district are distinctly sandy. Elsewhere in central Texas and in Trans-Pecos Texas the Taylor is of the type facies, i.e., marl or clay. In southern Arkansas the recorded Taylor equivalents are, in ascending order: Brownstown, dark gray, pure and slightly sandy marls; Ozan, dark gray sandy marl, chalky marl, glauconitic chalk, sandy marl and sands with black chert pebbles (sandier to east) ; Annona, white chalk; Marlbrook, dark gray pure and chalky marl. The Brownstown is lower Taylor; the middle Taylor is represented by the unconformity at the Brownstown-Ozan contact; and the Ozan, Annona and Marlbrook are upper Taylor. In the upper half of the Taylor the Annona-Pecan Gap-Marlin chalks, and at lower levels the Gober and the Lott, represent widespread conditions favorable to chalk deposition. The Anacacho is a near-shore limestone deposit of the reef facies.

Areal outcrop; local sections. —In Hunt, Fannin, Lamar and Red River counties, the Taylor is different from that in the type area in central Texas, and is subdivided into units which continue eastwards with some modification into southwestern Arkansas.